Splitting way breaks relations which are not downloaded

[Larry0ua]

Steps to reproduce the bug:

1. Download relation 1742393.
2. Select any node that is in the middle of the way.
3. Press P to split way.

Observed behavior:
way is splitted, but relations that use this way become broken as they now include only old part of the way, not new. Also, as these relations are not loaded to JOSM this situation is unable to solve in the client side.

Desired behavior one of the following:

• message box is shown saying "You are going to split way that is not downloaded completely. That may break relations using this way. Download way completely before splitting?" with buttons "Download" (green download icon), "Split without downloading" (no icon), "Cancel" (red cross icon - cancel default)
• some epsilon bounds around the point is downloaded and then way is splitted (not really preferred way to solve the ticket as is not obvious to the user)

[malenki]

Maybe related to #10838?

[skyper]

+1

default should be to request parent relations prior to split and deny splitting (if not in wiki:Help/ExpertMode).

[skyper]

Closed as duplicate of #18596.
There is already work done in #18596.

[skyper]

support for route, multipolygon and boundary has been added in #18596.
turn_restriction is covered in #10808.

If there are more unsupported types, please, open a new ticket.

[skyper]

Closed as duplicate of #17898.